1. Field of the Invention
This invention relates to the wireless transmission and reception of audio signals utilizing a modulated carrier RF signal. More particularly, it relates to the wireless transmission and reception of audio signals for a set of audio headphones wherein a modulated RF carrier signal in the 900 MHz range is employed to transmit the audio signals from a first stationary location (base unit) to a set of wireless audio headphones.
2. Background of the Prior Art
The transmission and reception of audio signals utilizing modulated RF carrier frequencies is well known in the prior art. The use of such technology to transmit audio signals from a base unit to a pair of wireless headphones is also known. In such use, the base unit is coupled to an audio processing device such as an audio receiver or amplifier which in turn is coupled to a CD player, phonograph player, radio receiver or other like audio producing device. The audio signal produced by one of these devices and processed by the audio receiver/amplifier is wirelessly transmitted to the audio headphones by way of the base unit coupled to the audio receiver/amplifier. High frequency carrier waves are employed wherein the audio information is modulated upon the high frequency carrier wave, transmitted by an antenna coupled to the base unit, received by a receiver unit (wireless headphones) also having an antenna, subsequently demodulated and thereafter converted to an audio signal which is reproducible by the wireless headphones.
The use of high frequency carrier waves in the 900 MHz range is known and became a standard for such wireless technology after the US government made the 900 MHz frequency range available for use by consumer electronic manufacturers. However, the manner in which these carrier frequencies are modulated and subsequently downconverted has remained complicated. One example can be seen in U.S. Pat. No. 6,215,981 to Borchardt et al. In such patent, a 900 MHz modulated RF carrier signal is used to transmit an audio signal from a base unit to a local receiving unit, such as, for example, a pair of wireless headphones. When the 900 MHz carrier frequency is received, it is downconverted a first time to an IF (intermediate frequency) of about 65 MHz. Thereafter, a second downconversion is affected to produce a lower frequency that can be reproduced by an electro acoustical transducer (the speakers within the pair of headphones). A standard FM radio receiver is coupled to the first downconverter and contains the second downconverter therewithin. The first downconversion converts the 900 MHz carrier signal to an intermediate frequency (IF) of 65 MHz signal. The second downconversion converts the signal to 10.7 MHz which is then demodulated into right and left audio signals which are reproducible by the electroacoustic transducers (speakers) of the wireless headphones. The second downconversion occurs in the standard FM radio receiver through the use of a VCO (voltage controlled oscillator) and a mixer. This prior art invention requires two downconversions, since the 65 MHz IF signal can not be demodulated into reproducible right and left audio signals. The 65 MHz IF signal is downconverted to a useable 10.7 MHz signal by the mixer after tuning the VCO to a suitable frequency level.
Since it would be desirous to simplify the transmission and reception process for this technology, improvements would be welcome. One such improvement could be to eliminate the need for two downconversions and hence the need for an IF carrier signal. This would certainly be an improvement in the art and represent a simplification of the transmission and reception process for wireless audio headphones.